Hybrid heating system and method

ABSTRACT

A hybrid heating system ( 10 ) and method in which an indoor coil ( 12 ) of a heat pump ( 14 ) is located upstream of a heat output of a non-electric second heat source ( 22 ), e.g., a gas or liquefied petroleum gas furnace. The heat pump ( 14 ) continues to operate even at low temperatures, i.e., below 0° F., and the non-electric second heat source ( 22 ) supplements the heat output of the heat pump ( 12 ) as needed to maintain a desired indoor temperature, thereby maximizing economic benefit from the heat pump ( 12 ).

FIELD OF THE INVENTION

The present invention relates to hybrid heating systems and methods. More specifically, the present invention concerns a hybrid heating system and method in which an indoor coil of a heat pump is located upstream of the heat output of a non-electric second heat source, e.g., a gas or liquefied petroleum gas furnace; the heat pump continues to operate even at low temperatures, i.e., below 0° F.; and the second heat source supplements the heat output of the heat pump as needed to maintain a desired indoor temperature, thereby maximizing economic benefit from the heat pump.

BACKGROUND OF THE INVENTION

Heat pumps operate by extracting heat from outdoor air, and transferring that heat to an enclosed space, such as a home or business. Heat pumps are generally more economical to operate than conventional furnaces that burn fossil fuels. However, as the temperature of the outdoor air decreases, the amount of extracted heat also decreases until a desired temperature within the enclosed space can no longer be maintained by operation of the heat pump alone. For this reason, some hybrid heating systems incorporate both a heat pump and a gas furnace, in which the heat pump is turned off at 35° F. and the furnace turned on in order to maintain the desired indoor temperature. The main reason that the heat pump is turned off is that its indoor coil is located downstream of the furnace, such that the heat pump's compressor would experience a damagingly high compression ratio due to the furnace-heated air flowing through the indoor coil. As a result, the economic advantage of the heat pump is completely lost below a threshold outdoor temperature, e.g., 35° F., at which the heat pump is turned off.

Hybrid systems incorporating a heat pump and an electric furnace are available in which the heat pump's indoor coil is located upstream of the electric furnace. Unfortunately, it is both time-consuming and expensive to reconfigure a building from gas to total electric heat. For example, gas furnaces provide higher-temperature air, require less airflow, and therefore use smaller ducts than electric furnaces. Reconfiguring a building from gas to total electric heat requires replacing the smaller ductwork, much of which may be very difficult to access, with larger ductwork to accommodate a larger volume of air. Reconfiguring a house from gas to electric heat also requires upgrading the electrical service by adding a large amount of additional electric capacity, e.g., 200 amperes, to the home's electric system.

Due to these and other problems and disadvantages in the prior art, a need exists for a hybrid heating system incorporating a heat pump and a non-electric second heat source, wherein the heat pump can continue operating even at low outdoor temperatures.

SUMMARY OF THE INVENTION

The present invention overcomes the above-identified and other problems and disadvantages by providing a hybrid heating system and method in which an indoor coil of a heat pump is located upstream of the heat output of a non-electric second heat source, e.g., a gas or liquefied petroleum gas furnace; the heat pump continues to operate even at very low temperatures, i.e., below 0° F.; and the second heat source supplements the heat output of the heat pump as needed to maintain a desired indoor temperature, thereby maximizing economic benefit from the heat pump.

In one embodiment, the heating system may comprise a heat pump having an indoor coil and operable to generate a first heat output; and a non-electric second heat source configured to provide a second heat output downstream of the indoor coil, wherein the heat pump and the second heat source operate substantially simultaneously when a demand for heat exceeds the first heat output of the heat pump.

In various implementations, the system may further comprise any one or more of the following features. The heat pump may be a high-efficiency two-stage heat pump having a coefficient of performance of 3. The non-electric second heat source may be a natural gas or liquefied petroleum (LP) gas furnace. The non-electric second heat source may be a high-efficiency variable capacity non-electric furnace operable to provide different amounts of heat so as to more closely supplement the first heat output of the heat pump. A first temperature sensor may be located downstream of the indoor coil and operable to monitor the first heat output and control operation of the heat pump. A blower may be located downstream of the indoor coil. A second temperature sensor may be located downstream of the non-electric second heat source's heat exchanger and operable to monitor the combined first and second heat outputs and monitor the temperature rise across the indoor coil and the heat exchanger of the non-electric second heat source.

These and other features of the present invention are described in greater detail below in the section titled DETAILED DESCRIPTION OF THE INVENTION.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The present invention is described herein with reference to the following drawing figures, which are not necessarily to scale:

FIG. 1 is a cross-sectional elevation view representation of an embodiment of the system of the present invention; and

FIG. 2 is a flowchart setting forth steps of an embodiment of the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawing figures, a system and method is herein described, shown, and otherwise disclosed in accordance with various embodiments, including a preferred embodiment, of the present invention.

Broadly, the present invention concerns a hybrid heating system 10 and method for reaching and maintaining a desired temperature in an enclosed space, in which an indoor coil of a heat pump is located upstream of the heat output of a non-electric second heat source, e.g., a gas or liquefied petroleum gas furnace; the heat pump continues to operate even at very low outdoor temperatures, i.e., below 0° F.; and the second heat source supplements the heat output of the heat pump as needed to maintain a desired indoor temperature, thereby maximizing economic benefit from the heat pump. Because the heat pump operates substantially continuously, and is only supplemented by the non-electric second heat source, the system 10 of the present invention is a true hybrid heating system, unlike prior art systems which operate one or the other heat source but not both simultaneously.

More specifically, with reference to FIG. 1, in one embodiment the system 10 may comprise a housing 11 having an intake opening A and an exhaust opening B; a first heat exchange coil 12, or “indoor coil”, associated with a heat pump 14; a first temperature sensor 16 located downstream of the first coil 12; a blower 18, or “air handler”, located downstream of the first sensor 16; primary and secondary heat exchangers 20A,20B associated with the non-electric second heat source 22 and located downstream of the blower 18; and a second temperature sensor 24 located downstream of the primary and secondary heat exchangers 20A,20B. Ductwork 26 for delivering the heated air may be connected to the exhaust opening B.

The heat pump 14 is operable to generate a first heat output at the indoor coil 12, which may be located substantially within the housing 11. The first temperature sensor 16 is operable to monitor the first heat output, and may be operable to control operation of the heat pump 14 with regard to reaching and maintaining the desired indoor temperature. The blower 18 is operable to push air in the downstream direction, and may also be located within the housing 11. The non-electric second heat source 22 is configured to introduce a second heat output within the housing 11 downstream of the indoor coil 12. The heat pump 14 and the second heat source 22 operate substantially simultaneously when the first heat output of the heat pump 14 is, by itself, insufficient to reach and maintain the desired indoor temperature. The second temperature sensor 24 is operable to monitor the combined first and second heat outputs, and may be operable to control operation of the second heat source 22 and the blower 18 with regard to reaching and maintaining the desired indoor temperature. Temperature sensors 16,24 may also be operable to protect the system 10 from overheating.

In one implementation, one, some, or all of the components of the system 10 may be substantially conventional. In one implementation, the heat pump 14 may be a high-efficiency two-stage heat pump having a coefficient of performance (COP) of 3 or better. In one implementation, the non-electric second heat source 22 may be a high-efficiency variable capacity non-electric furnace operable to provide different amounts of heat so as to more closely supplement the first heat output of the heat pump 14. In one implementation, the non-electric second heat source 22 is a natural gas or liquefied petroleum gas furnace. In one implementation, one or more of the components of the system 10 described above as being located within the housing 11 are located elsewhere, i.e., not fully or even partially within the housing 11.

With reference to FIG. 2, the invention may be characterized as a method comprising some or all of the steps of providing the heat pump 14 operable to generate the first heat output at the indoor coil 12, as shown in box 100; measuring the first heat output, and, as necessary, controlling operation of the heat pump 14 with regard to reaching and maintaining the desired indoor temperature, as shown in box 102; pushing the air in the downstream direction, as shown in box 104; introducing the second heat output of the non-electric second heat source within the housing 11 downstream of the indoor coil 12, as shown in box 106; operating only the heat pump 14 when the first heat output is, by itself, insufficient to reach and maintain the desired indoor temperature, as shown in box 108; operating the heat pump 14 and the non-electric second heat source 22 substantially simultaneously when the first heat output of the heat pump 14 is, by itself, insufficient to reach and maintain the desired indoor temperature, as shown in box 110; measuring the combined first and second heat outputs, and, as necessary, controlling operation of the second heat source 22 and the blower 18 with regard to reaching and maintaining the desired indoor temperature, as shown in box 112.

By way of example and not limitation, the system 10 may function substantially as follows. Air (indicated as AIRFLOW in FIG. 1) enters the intake opening A and flows over the indoor coil 12 of the heat pump 14, thereby transferring the first heat output of the heat pump 14. The first temperature sensor 16 monitors the temperature of the air downstream of the indoor coil 12. If operation of the heat pump 14 alone is sufficient to reach and maintain a desired indoor temperature of the space being heated, then the non-electric second heat source 22 is not engaged, and the air is blown out the exhaust opening B and into the ductwork 26 by the blower 18 and delivered to the space being heated. If operation of the heat pump 14 alone is not sufficient to reach and maintain the desired indoor temperature of the space being heated, then the non-electric second heat source 22 is engaged to provide a supplementary second heat output which, in combination with the first heat output provided by the heat pump 14, is sufficient to maintain the desired indoor temperature of the space being heated. The second temperature sensor 24 monitors the temperature of the air downstream of the non-electric second heat source 22. Blower speed control ensures proper and safe operating temperature across the indoor coil 12 and the heat exchangers 20A,20B. When it is necessary to defrost the heat pump 14, the system 10 may rely entirely on the non-electric second heat source 22 for heat, and to compensate for the cooling effect of the defrost cycle, until the heat pump 14 can be returned to the heating cycle.

Although the invention has been disclosed with reference to various particular embodiments, it is understood that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.

Having thus described the preferred embodiment of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: 

1. A heating system comprising: a heat pump having an indoor coil and operable to generate a first heat output; and a non-electric second heat source configured to introduce a second heat output downstream of the indoor coil, wherein the heat pump and the second heat source operate substantially simultaneously when a demand for heat exceeds the first heat output of the heat pump.
 2. The heating system as set forth in claim 1, wherein the heat pump is a high-efficiency heat pump having a coefficient of performance of 3 or better.
 3. The heating system as set forth in claim 1, wherein the non-electric second heat source is a natural gas furnace.
 4. The heating system as set forth in claim 1, wherein the non-electric second heat source is a liquefied petroleum gas furnace
 5. The heating system as set forth in claim 1, wherein the non-electric second heat source is a high-efficiency variable capacity non-electric furnace operable to provide different amounts of heat so as to more closely supplement the first heat output of the heat pump.
 6. The heating system as set forth in claim 1, further including a first temperature sensor located downstream of the indoor coil and operable to monitor the first heat output, and to control operation of the heat pump.
 7. The heating system as set forth in claim 1, further including a blower located downstream of the indoor coil.
 8. The heating system as set forth in claim 1, further including a second temperature sensor located downstream of a heat exchanger component of the non-electric second heat source.
 9. A heating system for heating an enclosed space to a desired temperature, the heating system comprising: a housing having an intake opening and having an exhaust opening located downstream of the intake opening; a heat pump operable to generate a first heat output, the heat pump having an indoor coil located substantially within the housing; a blower located within the housing and operable to push air in the downstream direction; and a non-electric second heat source configured to provide a second heat output within the housing downstream of the indoor coil, wherein the heat pump and the second heat source operate substantially simultaneously when a demand for heat exceeds the first heat output of the heat pump.
 10. The heating system as set forth in claim 9, wherein the heat pump is a high-efficiency heat pump having a coefficient of performance of 3 or better.
 11. The heating system as set forth in claim 9, wherein the non-electric second heat source is a natural gas furnace.
 12. The heating system as set forth in claim 9, wherein the non-electric second heat source is a liquefied petroleum gas furnace.
 13. The heating system as set forth in claim 9, wherein the non-electric second heat source is a high-efficiency variable capacity non-electric furnace operable to provide different amounts of heat so as to more closely supplement the first heat output of the heat pump.
 14. The heating system as set forth in claim 9, further comprising a first temperature sensor located downstream of the indoor coil and operable to monitor the first heat output, and to control operation of the heat pump.
 15. The heating system as set forth in claim 9, further comprising a second temperature sensor located downstream of a heat exchanger component of the non-electric second heat source.
 16. A heating system for reaching and maintaining a desired temperature of an enclosed space, the heating system comprising: a housing having an intake opening and having an exhaust opening located downstream of the intake opening; a heat pump operable to generate a first heat output, the heat pump having an indoor coil located substantially within the housing; a first temperature sensor located downstream of the indoor coil and operable to monitor the first heat output, and to control operation of the heat pump with regard to reaching and maintaining the desired temperature; a blower located within the housing and operable to push air in the downstream direction; a non-electric second heat source configured to introduce a variable second heat output within the housing downstream of the indoor coil, the non-electric second heat source having a heat exchanger, wherein the heat pump and the second heat source operate substantially simultaneously when the first heat output of the heat pump is, by itself, insufficient to reach and maintain the desired temperature; and a second temperature sensor located downstream of the heat exchanger of the non-electric second heat source and operable to monitor the combined first and second heat outputs, and to control operation of the non-electric second heat source and the blower with regard to reaching and maintaining the desired temperature.
 17. The heating system as set forth in claim 16, wherein the heat pump is a high-efficiency heat pump having a coefficient of performance of 3 or better.
 18. The heating system as set forth in claim 16, wherein the non-electric second heat source is a natural gas furnace.
 19. The heating system as set forth in claim 16, wherein the non-electric second heat source is a natural gas furnace. 